Abstract
Submerged macrophytes play an important role in structuring habitats and, therefore, in determining patterns of aquatic biodiversity. Because these plants are widespread in shallow areas of many Neotropical reservoirs, the present work investigated if variables related to habitat structure, measured in patches of submerged macrophytes (Egeria densa and E. najas), can be used to predict fish assemblage attributes (fish density and species richness). Based on patch characteristics at fine spatial extents (macrophyte patches within reservoir arms), we considered plant biomass, volume and proportional volume (i.e. percentage of macrophyte volume in the water column) as potential predictors. Fish and macrophytes were sampled with a 1-m² throw trap in littoral habitats of Rosana Reservoir, Paranapanema River, and simple correlation analyses were performed. Fish richness and abundance were highly correlated with all variables (R = 0.53 to 0.90), a relationship consistently observed in all sites. When compared to biomass, plant volume and proportional volume did not yield stronger correlations. We observed stronger correlations when E. densa and E. najas patches were analyzed separately (mono-specificity), probably because particular effects of each macrophyte on habitat structuring were removed (e.g. unnoticed morphological differences or unknown effects on habitat quality). The high R values observed in all pairwise relationships are uncommon in ecological studies, highlighting the predictive potential of variables related to habitat structure. These results suggest that, at small spatial extents, macrophyte biomass may represent an interesting predictor of fish density and richness in reservoirs with extensive colonization of submerged plants.
Highlights
Aquatic macrophytes are an ubiquitous group, in shallow aquatic environments
Because of the widespread distribution of macrophytes in aquatic ecosystems, and the predominance of small-sized fish species in South American reservoirs (Agostinho et al, 2007a), we evaluate if basic habitat characteristics can be used to predict fish assemblage attributes in littoral shores of a Neotropical reservoir, over a fine spatial extent
The present study showed that variables related to habitat structure in shallow shores were strongly correlated to attributes of fish assemblages in Rosana Reservoir, at the spatial extents and grains (1m2 quadrats) used in our work
Summary
Aquatic macrophytes are an ubiquitous group, in shallow aquatic environments. Because impounded rivers undergo significant modifications in landscape and hydrology at different spatial/temporal scales (Petts, 1984; Agostinho et al, 2007a; Mol et al, 2007), it is common that riverine habitats are lost or replaced by huge pelagic areas, which are unsuitable habitats for Neotropical fish fauna (Gomes & Miranda, 2001; Luz-Agostinho et al, 2006) In this case, habitat quality and quantity may increase dramatically when macrophyte species colonize littoral areas of reservoirs, by creating refuges against predation, new feeding sites, and spawning grounds. Recent studies in a Neotropical reservoir found that macrophyte patches with high plant biomass support high fish density and species richness (Pelicice et al, 2005) and constitute a feeding site for juveniles and adults (Casatti et al, 2003; Pelicice & Agostinho, 2006)
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